The present invention relates to a tensioning arrangement, and more particularly to a device for releasably securing the spindle neck of a manually held power drill in a slotted sleeve of an auxiliary tool unit.
The versatility of the widely owned hand-held electric drills has been vastly increased in recent years by providing auxiliary tool units, such as circular saws, sanders, power planes, routers and the like, which can be connected with the power drill that serves as the power source for them and serves to drive them. As a general rule, this connection which must of course be releasable, is effected by inserting the spindle neck of the power drill into a slotted sleeve of the auxiliary tool unit, and thereupon tensioning the sleeve against the spindle neck to connect the tool by friction. For this purpose there is provided at each side of the axial slot in the sleeve of the auxiliary tool unit an eyelet which receives a tensioning screw that acts in direction tangentially of the slotted sleeve so that, when the screw is tightened, it draws the two eyelets together and tends to decrease the width of the slot, thus pulling the sleeve tightly against the spindle neck of the power drill.
This arrangement is satisfactory if the housing and sleeve of the auxiliary tool unit are made of metallic material. There is, however, a recent trend towards manufacturing the housing and sleeve of synthetic plastic material, usually thermoplastic material. It has now been found that if thermoplastic materials are used, the previously satisfactory manner of connecting the slotted sleeve of the auxiliary tool unit to the spindle neck of the power drill is no longer properly usable. The reason for this is that thermoplastic material when subjected to the tensioning stresses necessary to push the sleeve against the spindle neck of the drill, tends to flow or yield sufficiently so that the mechanical tension becomes decreased to the point where the drill and the auxiliary tool unit are no longer connected with one another reliably enough to provide a proper transmission of power and to eliminate the possibility of hazzards due to undesired and accidental disconnection. Thus far the prior art has proposed to surround the slotted sleeve with a tension band analogous to a conventional hose clamp which has two end portions formed with the respective eyelets and through which the tensioning screw extends. The eyelets are therefore no longer present in the material of the slotted sleeve itself, and the difficulties encountered in proper tensioning where the slotted sleeve was of synthetic plastic material, have been overcome.
However, where the slotted sleeve is of synthetic plastic material, even this arrangement does not overcome all problems. The tensioning of the band is relatively difficult because the screw must be turned through quite a substantial distance before sufficient tension is exerted by the band upon the slotted sleeve. It is well known, of course, that a slotted sleeve of synthetic plastic material will yield more substantially than a similar sleeve of metallic material. Also, the angled ends of the tensioning band itself, in which the eyelets for the screw are formed, tend to yield as the screw is being tightened and all of this results in the necessity for the screw to be turned through quite substantial distances before the desired tensioning is obtained. This is time consuming, and necessitates the use of at least simple tools such as a screwdriver, and at times may be quite frustrating for the inexperienced do it yourself home worker who is the person most likely to employ these power tool combinations.